David - how right you are! I took off the rapido couplers and installed the microtrain knuckles and have yet to modify that trip pin. It catches most of the time...I had bent them just slightly more but I'm considering just cutting most of the forward facing metal off and leaving a much small trip pin to hold the coupler together.
Of course - I'm also thinking of switching one engine's Nscale couplers for a Zscale just as a test. Just got done reading the article on MRR about that...so armed with a very little knowledge, I might give it a go.